Wrought nickel-base alloy and products thereof

ABSTRACT

1. A WROUGHT NICKEL-BASE SUPERALLOY ARTICLE HAVING A NOMINAL CHENISTRY WHICH CONSISTS ESSENTIALLY OF, ABOUT BY WEIGHT, 12.4 PERCENT CHROMIUM, 18.5 PERCENT COBALT, 3.2 PERCENT MOLYBDENUM, 4.3 PERCENT TITANIUM, 5 PERCENT ALUMINUM, 0.8 PERCENT VANADIUM, 0.02 PERCENT VORON, 0.06 PERCENT ZIRCONIUM, 0.07 PERCENT CARBON, BALANCE ESSENTIALLY NICKEL, AND CHARACTERIZED BY V-NOTCH STRENGTHENING IN THE TEMPERATURE RANGE OF 1300* -1400* F.

United States Patent O 3,843,421 WROUGHT NICKEL-BASE ALLOY AND PRODUCTSTHEREOF Arthur R. Cox, Lake Park, Fla., Paul R. Holiday, Haverstraw,N.Y., and Gary K. Lewis, Riveria Beach, and Sven D. Soderquist, PalmBeach Gardens, Fla., assignors to United Aircraft Corporation, EastHartford, Conn. No Drawing. Filed Oct. 16, 1972, Ser. No. 298,068

Int. Cl C22c 19/00 US. Cl. 148-32 3 Claims ABSTRACT OF THE DISCLOSURE Astrong nickel-base superalloy is provided which displays good hightemperature mechanical properties, including notch ductility, in wroughtform when formulated to a very precise composition.

This invention was made in the preformance of a contract with theDepartment of the Air Force.

BACKGROUND OF THE INVENTION This invention relates to the high strengthnickel-base superalloy field.

In the patent to Bieber 3,061,426 there is disclosed a nickel-base alloyof the 7-7 type which has for some time been extensively used in castform in gas turbine engine blade applications. In such form, this alloyhas been typically formulated to the nominal chemistry consisting of, byweight, 9.5 percent chromium, 15 percent cobalt, 3 percent molybdenum,4.8 percent titanium, 5.5 percent aluminum, 1 percent vanadium, 0.015percent boron, 0.06 percent zirconium, 0.17 percent carbon, balancenickel.

As originally developed and utilized, the strength and ductility of thealloy were such that it was practically undeformable and, hence, foundapplication only in precision cast form and found utility only in thoseapplications, such as turbine blades, where cast properties wereacceptable. With the generation of the forging process described in thepatent to Moore et al. 3,519,503 means were provided whereby the alloycould, if desired, be readily forged, including forging to shapes suchas engine discs as well as miscellaneous other forms such asshafts,rings and seals. Because the high temperature strength/low densitycharacteristics are so favorable for aerospace applications, seriousconsideration was given to the expanded use of the alloy, particularlyfor engine discs. Unfortunately, the mechanical property criteriaapplicable to discs differ in some respects from those required inblades and, although satisfactory performance was attained with theconventional alloy in cast form as blading, it was unsatisfactory inwrought form in engine discs.

In a gas turbine engine, the blades are typically retained in fir treenotches machined in the periphery of the disc. The disc must, therefore,not display unacceptable notch sensitivity. For an acceptable discalloy, the presence of a notch should not result in a decrease instrength at the notch, vis-a-vis the unnotched specimen of the samedimensions as the notch. Preferably, in fact, the distribution of forcesand alloy characteristics should be such that notch strengthening isexhibited. Unfortunately, at the usual specification composition thenotch strength of the conventional alloy was less than that of thesmooth specimen, particularly in the critical 1300-1400 F. temperaturerange to which the periphery of the disc may become heated in operation.

Thus, although the alloy could be formed into disc form, the utility insuch form was limited.

SUMMARY OF THE INVENTION The present invention is directed to a wroughtnickelbase superalloy of critical composition and wrought productsproduced therefrom, which, upon suitable heat treatment, produces aspecific volume of the strengthening 7' phase, typically Ni (Al,Ti)together with a carbide, including the M C -type carbide, which not onlymaintains acceptable levels of other mechanical and physical propertiesbut also provides notch strengthening, particularly in the 13001400 F.temperature range.

The wrought alloy is provided at a nominal chemistry of, by weight, 12.4percent chromium, 18.5 percent cobalt, 3.2 percent molybdenum, 4.3percent titanium, 5.0 percent aluminum, 0.8 percent vanadium, 0.02percent boron, 0.06 percent Zirconium, 0.07 percent carbon, balanceessentially nickel. 1

Forged products produced to the foregoing chemistry display notchstrengthening in the 1300-1400 F. temperature range with oxidationresistance to at least 1600" F. when heat treated as follows:

The fully heat treated article is characterized by a 7' volumepercentage of about 50-60 percent, preferably about 56 volume percent,as compared to a more typical 70 volume percent in the usual cast alloychemistry.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As previously mentioned, theconventional alloy was developed for and used in the production ofcastings exhibiting high temperature strength and oxidation resist ance.The present invention contemplates wrought component applications andhas been developed to produce, upo favorable heat treatment, a specificvolume of intermetallic precipitates of the 'y' and M C types whichprovide the requisite mechanical properties, including in particularnotch strengthening, in the general temperature range of 1300l400 F.This is distinct from the criteria and microstructure used for andpresent in the prior castings and in wrought components formulated tothe same composition as such castings.

The composition, which was found to be critical in several essentialrespects, is as follows, by weight: 11.9- 12.9 percent chromium, 18-19percent cobalt, 2.8-3.6 percent molybdenum, 4.1-4.5 percent titanium,4.8-5.2 percent aluminum, 0.5-1 percent vanadium, 0.016-0.024 percentboron, 0.04-0.08 percent zirconium, 0.05-0.09 percent carbon, balanceessentially nickel.

The full preferred heat treatment specified is as follows.

Property criteria minimums are typically as follows:

(a) tensile properties (fully heat treated forgings).

Room temperature 1300 F.

Tensile strength; p.s.i 220,000 170, 000 Yield strength at 0.2% offset,p.s.i 145, 000 145, 000 Elongation, percent in 4D 12 12 Reduction ofarea, percent 15 15 (b) hardnessBrinell 321-414.

(c) stress-rupture (combination smooth/material specimen)-forging heldat 1350 F. under continuously applied axial load of 100,000 p.s.i. shallnot rupture in less than 23 hours.

(d) creep rupture-with a smooth specimen at 1300" F. and continuouslyapplied axial load of 85,000 p.s.i., time to 0.2% plastic deformationshall average not less than 150 hours with no value below 110 hours.

Table I provides a comparative distributional analysis of the presentinvention and the conventional composition in terms of their respectivephysical properties.

TABLE I.-PROPERTY DISTRIBUTION ANALYSIS RIP. tensile (k.s.i.)

Conventional composition This invention Percent Percent Percent PereenYS UTS RA. YS UT el. 11.11.

1,300 F. tensile Conventional composition This invention Percent PercentPercent Percent YS UTS el. R. YS UTS e1. RA.

Stress rupture (smooth) (1350 F./100 k.s.i.)

Stress rupture (V -noteh) 0.2% creep (1300 F./88 Conventional (1350F./100 k.s.i.) k.s.i.)

composition This invention Conventional This Conventional This PercentPercent composition, invention, composition, invention, Hrs. el. Hrs el.hrs. hrs. hrs. hrs.

1 Distribution appears abnormal. 9 Greater than smooth. 1 150 avg, 110min.

From the foregoing Table, it will readily be seen that the alloy of thepresent invention provides the requisite notch strengthening forsensitive forged or extruded components whereas forgings made from theconventional alloy were unacceptably deficient in this regard. Thisfactor alone is determinative of the utility of the alloy in componentssuch as turbine engine discs. And it is only within the criticalitylimits of the present invention that the necessary properties have beenachieved, providing an article having properties never beforereproducibly attained.

In the cast alloy previously used, the 7' content has generally beenabout 70 volume percent or higher. The wrought alloy composition of thepresent invention provides a microstructure having about -60 volumepercent of the strengthening '7' phase, with about 56 volume percentappearing optimum. Thus, in the composition of the present invention,the total aluminum plus titanium content of the alloy is especiallycritical insofar as these elements are the principal determinants of theamount of the 7 phase which is formed.

Further, in the alloy two carbide phases appear present, including a CrC carbide distributed along grain boundaries and a TiC carbidedistributed intragranularly. The Cr C carbide precipitated at the grainboundaries is the phase of importance to the present invention for itproduces a region of localized plasticity which can undergo microstrainand provide the necessary delay to failures attributable to grainboundary efiects. Thus, the carbon content is especially critical inthis alloy.

What is claimed is:

1. A wrought nickel-base superalloy article having a nominal chemistrywhich consists essentially of, about by weight, 12.4 percent chromium,18.5 percent cobalt, 3.2 percent molybdenum, 4.3 percent titanium, 5percent aluminum, 0.8 percent vanadium, 0.02 percent boron, 0.06 percentzirconium, 0.07 percent carbon, balance essentially nickel, andcharacterized by V-notch strengthening in the temperature range of13001400 F.

2. An article according to claim 1 which is also characterized by amicrostructure in the fully heat treated condition exhibiting 50-60volume percent of a 'y' intermetallic phase.

3. An article according to claim 2 wheerin the article is a gas turbineengine component.

References Cited UNITED STATES PATENTS 3,061,426 10/1962 Bieber 75--17l3,519,503 7/1970 Moore et a1 148-115 F 3,642,469 2/1972 Ross et a1.75171 RICHARD O. DEAN, Primary Examiner US. Cl. X.R.

1. A WROUGHT NICKEL-BASE SUPERALLOY ARTICLE HAVING A NOMINAL CHENISTRYWHICH CONSISTS ESSENTIALLY OF, ABOUT BY WEIGHT, 12.4 PERCENT CHROMIUM,18.5 PERCENT COBALT, 3.2 PERCENT MOLYBDENUM, 4.3 PERCENT TITANIUM, 5PERCENT ALUMINUM, 0.8 PERCENT VANADIUM, 0.02 PERCENT VORON, 0.06 PERCENTZIRCONIUM, 0.07 PERCENT CARBON, BALANCE ESSENTIALLY NICKEL, ANDCHARACTERIZED BY V-NOTCH STRENGTHENING IN THE TEMPERATURE RANGE OF 1300*-1400* F.